The invention relates to a digital wireless communication system. In particular, the invention relates to cordless telephones and cellular networks.
A common type of wireless communication is the communication which occurs between a cordless telephone handset and its associated base unit within a limited distance range around the user""s home or business. Cordless telephones typically operate over a radio frequency (RF) portion of the spectrum set aside for general public use. Also, the power of the cordless phone signal is lower than other communication signals, because the signal needs to only be transmitted between the cordless handset and the associated base unit within the home or business of the user. Therefore, there is no user license from the Federal Communications Commission (FCC) required to operate a cordless telephone. Ultimately the communication is carried from the associated base unit along a landline on the public telephone network to the connecting party; therefore the cost of the telephone call is regulated by the LEC which owns the public switched telephone network (PSTN).
Another method of wireless communication is a regional cellular communication network which is operated by a cellular operator to enable the transmission of voice and data from a mobile station to a cellular base station over a specific band of frequencies, e.g., 824-849 MHz and 869-894 MHz, under license by the FCC. The bands are generally broken up into transmission channels and reception channels which each employ different bands of frequencies in the cellular spectrum. Cellular transmissions from the base station to the mobile station occupies the spectrum between 824 and 849 MHz with each transmission channel occupying about 30 KHz. Cellular reception from the mobile stations to the base stations generally occupy the spectrum between 869 and 894 MHz with each reception channel occupying about 30 KHz. As is well known to those of ordinary skill in the art, each of the transmission and reception bands are divided between two cellular service providers in each market and are referred to as xe2x80x9cAxe2x80x9d and xe2x80x9cBxe2x80x9d bands. Thus, each provider operates four hundred and sixteen pairs of transmission and reception frequency channels on which to provide service. Twenty-one of the four hundred and sixteen frequency channels pairs are ordinarily used as control channels to send control signals from the base station to the mobile station, thus only three hundred and ninety-five channels are actually available to transmit calls between the cellular base station and mobile station. The cellular service provider enlists subscribers who are authorized to communicate via the regional cellular network. Each subscriber must purchase a mobile station or handset which is capable of communication with the regional cellular network. The handset, at the time of manufacture, is assigned an electronic serial number (ESN). The ESN is generally stored in the permanent memory, such as an EEPROM, in the handset. The subscriber registers the mobile station with the regional cellular network and the mobile station is assigned a mobile identification number (MIN) by which the mobile station can be accessed. As the price of mobile stations decreases and the cost of air time decreases, the number of users that subscribe to regional cellular networks is increasing.
Recently, handsets have been disclosed which are capable of switching between communication with a cellular network and with an RF cordless telephone unit. Once the handset is in the proximity of the cordless telephone unit, the telephone unit is capable of receiving calls from both the public switched telephone network (via the RF cordless telephone unit) and the regional cellular network. Since the cellular and RF cordless communication systems utilize different frequency bands for communication, a handset that can communicate with both cellular and RF cordless base stations requires some significant additional hardware and software. In practice, a handset that can communicate with both types of base stations requires one transceiver that can communicate with cordless frequencies and one transceiver that can communicate with cellular frequencies as well as separate interface hardware between each transceiver and the main handset controlling hardware. Further, the main handset controlling hardware must be able to recognize and communicate with the different communications protocols required to communicate with the RF cordless telephone base station and with the cellular networks. The additional hardware required to communicate with both base stations increases the size and the weight of the handset. Further, the additional hardware increases the cost of the handset in a highly price-competitive market.
The preferred embodiment of the present invention comprises a cordless cellular base system. A cordless cellular base station is capable of communicating with a cellular network compatible mobile unit, also referred to as a mobile station herein. The cordless cellular base station, also referred to as a subregional basestation, is preferably connected to a landline on a public switched telephone network and is assigned a landline number or phone number. The mobile station is registered with a cellular network and is assigned a mobile identification number. Advantageously, the mobile station is capable of communication with both a conventional regional cellular base station and to the cordless cellular base station utilizing the same cellular frequency range and communications protocol.
One preferred method of controlling a base station comprises the steps of initially registering with the cellular network, registering the mobile telephone to receive telephone service through the base station upon being detected by the mobile telephone, wherein the mobile telephone, while operating in a cellular mode and communicating via the cellular network, detects the base station using the base station operating power levels to recognize locations that are in proximity to the base station and searches for the base station using stored base station identification information when in proximity to the base station, wherein the mobile telephone automatically de-registers with the cellular network upon detecting the base station, receiving confirmation that the mobile telephone has automatically switched from providing cellular service to providing cordless landline service.
The method further provides a call forwarding update message to the cellular network upon receiving the confirmation, the message requesting re-routing of calls addressed to the mobile telephone from the cellular network to the PSTN telephone number, receiving a forwarded call addressed to the mobile telephone, determining a status of the mobile telephone in response to the received call, selecting a call information message in response to the status, sending the call information message to the mobile telephone, and transferring the forwarded call to the mobile telephone via a wireless link in response to receipt of a user response to the call information message.
Other features of the preferred method of controlling a base station include the steps of receiving a mobile station identification number from the mobile telephone which is received by the base station upon detection of the base station by the mobile telephone, comparing the received mobile station identification number with a list of mobile station identification numbers stored in the base station, wherein the mobile station identification numbers of the list each correspond to mobile stations registered with the base station, and processing communications from the mobile telephone in response to a match between the received mobile station identification number and an entry of the list of mobile station identification numbers resulting from the comparison.